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UCC28634: ACon and ACoff threshold

Ermanno Di Criscio
Prodigy 30 points
Part Number: UCC28634
Other Parts Discussed in Thread: UCC28700

Dear supporters,

I need some explanation on  ACon and ACoff parameters for UCC2863x controller.

They should indicate minimum and maximum AC (or DC if multiplied by sqrt(2)) input voltage to start or stop IC operation, but i don't understand how to use the provided parameters.

The input voltage (voltage on bulk capacitor) is sensed by auxiliary winding of power transformer during Ton of power switch shifting the sensed voltage with the suggested resistor/diode circuit, but in section 8.4.1 of datasheet, the first two parameters in table 6 refer to line voltage. Is this data provided by assuming fixed transformer turns ratio? What is the equivalent sensed threshold voltage?

  • 0
    TI__Guru* 75565 points

    Hello,

    I found the equations in the Mathcad file for the following link for setting up resistors Ra, Rb and Rp for UV lockout.

    These same equations were used in the excel design tool as well.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 30 points

    Hi Mike O', thanks for your answer

    This two equatins are already in the datasheet, in section 8, but i'd like to know if i can make some trick to push the input UV down to 24 Vdc. These equations sey how to compute Ra and Rb and the limit that their thevenin equivalent must have to eliminate startup problems, but they don't provide any information about Vsense threshold or operation when controller makes inspection pulses to measure input voltage.

    I'd like to use this controller in flyback project with input voltage from 24 Vdc to 320 Vdc. I actually seeing for UCC28700, but i like safety function that ucc2863x provide and i think using it the project can be cheaper considering that it need few components comparaed to ucc28700.

  • 0 in reply to Ermanno Di Criscio
    TI__Guru* 75565 points

    Hello,

    The UCC28700 should have similar protection functions compared to the UCC28636.  The input under voltage is easier to setup. The device has OCP, OVP and input UVLO shutdown.

    I found this UCC28700 reference design that has an input of 25VDC and 520VDC

    Regards,

  • 0 in reply to Mike O'
    Prodigy 30 points

    Hi Mike,

    Mike O' said:

    Hello,

    The UCC28700 should have similar protection functions compared to the UCC28636.  The input under voltage is easier to setup. The device has OCP, OVP and input UVLO shutdown.

    I found this UCC28700 reference design that has an input of 25VDC and 520VDC

    Regards,

    that's the reason why i'm looking for it, but it need more components, anyway i'll use it.

    Regards